With a rapid growth of the wireless mobile communication market, a demand for a diversity of multimedia services in the wireless environment is made. In order to provide multimedia services, a research for multi-antenna systems (e.g., Multiple Input Multiple Output (MIMO) systems) achieving a large capacity of transmit data and a high speed of data transmission while being able to efficiently utilize the limited frequency resources is made.
A multi-antenna system transmits data using an independent channel by antenna and thus, can increase transmission reliability and a transmission rate compared to a single antenna system even without additional frequency or additional transmit power. Also, the multi-antenna system allows several users to simultaneously share space resources secured through a multiple antenna, thus being able to more increase frequency efficiency.
A multi-antenna system of a multiple user environment uses beamforming to cancel interference between users. For example, if the multi-antenna system uses coordinated beamforming to cancel interference between users, a transmit end generates a precoding weight and post-processing weight using downlink channel information. The precoding weight and post-processing weight have vector or matrix values.
If the multi-antenna system uses coordinated beamforming as above, the transmit end transmits a post-processing weight to a receive end. The transmit end transmits a post-processing weight to the receive end using a dedicated pilot or a feedforward channel.
In the case of using a dedicated pilot, there is a problem that, because the transmit end allocates the dedicated pilot to avoid pilot superposition at each receive end, a pilot overhead increases.
In the case of using a feedforward channel, there is a problem that, because the transmit end quantizes a post-processing weight for each receive end and transmits the quantized post-processing weight over the feedforward channel, a feedforward channel capacity increases in proportional to number of receive ends.
Also, in the case of reducing an amount of information transmitted over a feedforward channel from a transmit end, there is a problem that a quantization error increases and thus a throughput decreases.